Mitosis and the Cell Cycle Subtitle Cell Division

Mitosis and the Cell Cycle Subtitle

Cell Division

Where do cells come from? And what’s in charge of making those new cells? • All cells come from existing cells • New cells are produced for growth and to replace damaged or old cells • DNA contains the instructions for making cell parts • So each new cell must get a complete set of the DNA

DNA Replication • DNA must be copied or replicated before cell division • Each new cell will then have an identical copy of the DNA Original DNA strand Two new, identical DNA strands

Prokaryotic Cell Division • Prokaryotes divide into 2 identical cells by the process of binary fission • Single chromosome makes a copy of itself • Cell wall forms between the chromosomes dividing the cell

Prokaryotic Chromosome • The DNA of prokaryotes is one, circular chromosome attached to the inside of the cell membrane

Eukaryotic Cell Division • What’s more complicated about it? Why? • How do all the DNA and organelles know where to go?

Eukaryotic Chromosomes • All eukaryotic cells store genetic information in chromosomes • Most eukaryotes have between 10 and 50 chromosomes in their body cells • Human body cells have 46 chromosomes • 23 homologous pairs

Eukaryotic Chromosomes • When not dividing: DNA and protein uncoiled – called chromatin • When dividing: DNA and protein tightly condense – called chromosome

When Cells Divide, Chromosomes Condense • Duplicated chromosomes are called chromatids and are held together by the centromere

The Cell Cycle

What happens in a cell’s lifetime? What do cells spend most of their time doing?

The Cell Cycle • G 1 – primary growth phase • S – synthesis; DNA replicated • G 2 – secondary growth phase Collectively these 3 above stages are called Interphase • M - mitosis • C - cytokinesis

Interphase – G 1 Stage • 1 st growth stage after cell division • Cells mature by making more cytoplasm & organelles • Cell carries on its normal metabolic activities

Interphase – S Stage • Synthesis stage • DNA is copied or replicated

Interphase – G 2 Stage • 2 nd Growth Stage • Occurs after DNA has been copied • All cell structures needed for division are made (e. g. centrioles) • Both organelles & proteins are synthesized

Steps of Mitosis Eukaryotic Cell Division

Mitosis • Division of the nucleus • Also called karyokinesis • Only occurs in eukaryotes • Has four stages • Doesn’t occur in some cells such as brain cells 1 2 3 4 4 Stages: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

Early Prophase • Chromatin in nucleus condenses to form visible chromosomes • Mitotic spindle forms from fibers in cytoskeleton or centrioles (animal) Nucleolus Cytoplasm Nuclear Membrane Chromosomes

Late Prophase • Nuclear membrane & nucleolus are broken down • Chromosomes continue condensing & are clearly visible • Spindle fibers called kinetochores attach to the centromere of each chromosome • Spindle finishes forming between the poles of the cell Chromosomes Nucleus & Nucleolus have disintegrated

Spindle Fiber Attached to Chromosome Kinetochore Fiber Chromosome

Metaphase

Metaphase • Chromosomes, attached to the kinetochore fibers, move to the center of the cell • Chromosomes are now lined up at the equator Equator of the cell Pole of the Cell

Metaphase

Metaphase Review What the cell looks like What’s occurring

Anaphase • Sister chromatids are pulled apart to opposite poles of the cell by kinetochore fibers • Occurs rapidly

Anaphase Sister Chromatids being separated

Anaphase Review What the cell looks like What’s occurring

Telophase • Sister chromatids at opposite poles • Spindle disassembles • Nuclear envelope forms around each set of sister chromatids • Nucleolus reappears • CYTOKINESIS occurs • Chromosomes reappear as chromatin

Cytokinesis • Means division of the cytoplasm • Division of cell into two, identical halves called daughter cells • In plant cells, cell plate forms at the equator to divide cell • In animal cells, cleavage furrow forms to split cell

Cytokinesis Cleavage furrow in animal cell Cell plate in plant cell

Daughter Cells of Mitosis • Have the same number of chromosomes as each other and as the parent cell from which they were formed • Identical to each other, but smaller than parent cell • Must grow in size to become mature cells (G 1 of Interphase)

Eukaryotic Cell Division • Used for growth and repair • Produce two new cells identical to the original cell • Cells are diploid (2 n) Prophase Metaphase Anaphase Chromosomes during Metaphase of mitosis Telophase Cytokinesis

THE END!